<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8">
  <title>监听属性</title>
  <script src="vue.js"></script>
</head>

<body>
  <div id="app">
    千米 : <input type="text" v-model="kilometers">
    米 : <input type="text" v-model="meters">
  </div>
  <p id="info"></p>
  <script type="text/javascript">
    const app = Vue.createApp({
      data() {
        return {
          kilometers: 0,
          meters: 0
        }
      },
      watch: {
        kilometers: function (val) {
          this.kilometers = val;
          this.meters = this.kilometers * 1000
        },
        meters: function (val) {
          this.kilometers = val / 1000;
          this.meters = val;
        }
      }
    });

    app.mount('#app')
  </script>
</body>

</html>